1. Field of the Invention
This invention relates to apparatus using substantially amorphous magnetic compositions having uniaxial magnetic anisotropy.
2. Description of the Prior Art
Amorphous materials are known in the art and can generally be classified as either metals or non-metals. The metals are described by either the Bernal model (where dense random packing exists) or by microcrystalline models. Amorphous metallic materials include Pd-Si and Mn-C alloys.
Non-metallic amorphous materials are generally covalently bonded and are exemplified by the "ovonic-type" materials. They are explained by random network models or by microcrystalline models in which the existence of atomic ordering is over distances less than 25A. Non-metallic amorphous materials are exemplified by SiO.sub.2, Si, Ge, and Ge-Te alloys.
Non-metallic amorphous materials have been used for various applications including beam addressable information storage, as can be seen by referring to U.S. Pat. No. 3,530,441. However, the prior art does not show the use of amorphous magnetic materials having uniaxial anisotropy in applications such as magneto-optic devices and bubble domain systems. Additionally, the use of amorphous magnetic materials as permanent magnets is also not shown in the art. Such materials would be of value in a variety of applications such as this. For instance, amorphous materials can be deposited on any type of substrate and do not have to be lattice-matched with the substrate. Further, intrinsic substrate defects are not detrimental to the properties of the subsequently deposited amorphous material.
Additional advantages of amorphous materials include the fact that their compositions can be adjusted to optimize their properties without the restrictions imposed by compound stoichiometry That is, restrictions imposed by phase diagrams of materials to be combined are not present when amorphous materials are made. Additionally, amorphous materials can be prepared at low temperatures and fabricated by simple techniques such as evaporation, sputtering, etc.
Particularly with regard to magnetic amorphous materials, structural defects in the amorphous materials do not exist which would impede movement and nucleation of magnetic domains in the material. Also, these materials can have compositions which change over wide ranges to enhance selected magnetic properties. The addition of impurities to the composition will not affect the structural or magnetic properties in the films in an adverse way and can be used to obtain greater flexibility of composition design.
Amorphous films comprising multicomponent systems have been discussed in the literature. For instance, Sawatzky et al, Journal of Applied Physics, 42, 1, Jan. 1971, pg. 367, describes the kind of films which are amorphous when sputtered and then crystalline after an annealing process. In a related paper (Material Science Research, Vol. 4, pg. 493, 1969) E. Giess et al describes gadolinium iron garnet films having crystallite sizes between 30 and 50A. A ferromagnetic amorphous film comprising Fe-C-P alloy is described in Duwez et al, Journal of Applied Physics, 38, 10, Sept. 1967, p. 4096. The amorphous films described in these references do not exhibit uniaxial magnetic anisotropy.
Amorphous magnetic films of Fe.sub.x Gd.sub.y are described in J. Orehotsky et al, Journal of Applied Physics, 43, 5, May 1972, pg. 2413. In order to explain nonsaturation in these films, the authors proposed the existence of a perpendicular anisotropy associated with an isotropic stress in the plane of the film.
In the present invention, it has been discovered that uniaxial anisotropy can be produced in amorphous magnetic films and that anisotropy can be produced independent of substrate constraints. That is, uniaxial anisotropy can be obtained through pair ordering or through shape induced anisotropy. These amorphous compositions can be comprised of a single element or of a plurality of elements. Use of these amorphous magnetic compositions in device applications overcomes many of the disadvantages of prior art devices where crystalline magnetic material had to be used.
Accordingly, it is an object of the present invention to provide magnetic devices using substantially amorphous magnetic compositions.
It is another object of this invention to provide devices and systems using substantially amorphous magnetic compositions whose properties can be tailored over wide ranges.
It is still another object of this invention to provide magnetic bubble domain systems using amorphous magnetic materials for support of the magnetic bubble domains.
It is a still further object of this invention to provide magnetic bubble domain apparatus in which domains can be easily propagated without regard to structural defects or impurities in the material supporting the bubble domains.
It is a further object of this invention to provide magneto-optic systems using amorphous magnetic materials for modulation of light beams.
It is another object of this invention to provide devices using magnetic domains which can be fabricated easily and with reduced cost.